Advanced Database Management System - Tutorials and Notes: Full partial transitive and multivalued function dependencies

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## Various Types of Functional Dependencies used in Normalization Process

 Full Functional Dependency – Click here to read more… Definition 1: If X is a set of attributes and Y is another set of attributes, then any functional dependency such that X → Y is said to be a full functional dependency if and only if all the attributes of Y is functionally dependent on complete X. In other words, X → Y becomes invalid if we remove any attribute from X. Definition 2: A functional dependency X → Y is a full functional dependency if removal of any attribute from A results in the dependency no longer existing Functional Dependency – Click to read more… Functional dependency is a constraint (condition) that describes the relationship between two sets of attributes. It is written as X → Y. it can be read as, the values of X determine the values of Y uniquely, or the values of Y are uniquely determined by the values of X, or Y is functionally dependent on X. Here, X is determinant, and Y is dependent. Multi-valued Dependency– Click to read more… Partial Dependency It is a type of functional dependency where a non-key (non-prime) attribute is functionally dependent on a subset of the primary key (or candidate key) attribute. For example, we would say that a functional dependency XY → A as a partial functional dependency, if there exists other FDs like X → A or Y → A. In other words, removal of Y from X → A or removal of X from Y → A still holds the dependency. Transitive Dependency – Click to read more… Dependency of a non-key attribute (or set of non-key attributes) on another non-key attribute (or set of non-key attributes) is called transitive dependency. For example, if X → Y and  Y → Z holds in a relation R(X, Y, Z), then these FDs imply X → Z (through transitivity axiom). Then X → Z is called transitive dependency. Trivial Functional Dependency – Click to read more… The dependency of an attribute (or set of attributes) on a set of attributes is called trivial functional dependency if the set of attributes on the Left Hand Side (LHS) of the functional dependency contains RHS attributes. In other words, a functional dependency A → B is said to be trivial if B is subset or equal to A. Other examples are X → X, Y → Y, AB → AB etc.

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